U.S. patent number 8,441,085 [Application Number 12/849,675] was granted by the patent office on 2013-05-14 for method of manufacturing electronic apparatus and electronic apparatus.
This patent grant is currently assigned to Japan Display West Inc.. The grantee listed for this patent is Yasuhiro Kanaya, Yasuo Mikami, Yoshifumi Mutoh, Koichi Nagasawa, Nobutaka Ozaki, Hirohisa Takeda, Takashi Yamaguchi. Invention is credited to Yasuhiro Kanaya, Yasuo Mikami, Yoshifumi Mutoh, Koichi Nagasawa, Nobutaka Ozaki, Hirohisa Takeda, Takashi Yamaguchi.
United States Patent |
8,441,085 |
Nagasawa , et al. |
May 14, 2013 |
Method of manufacturing electronic apparatus and electronic
apparatus
Abstract
An electronic apparatus having a substrate with a bottom gate
p-channel type thin film transistor; a resist pattern over the
substrate; and a light shielding film operative to block light
having a wavelength shorter than 260 nm over at least a channel
part of said thin film transistor.
Inventors: |
Nagasawa; Koichi (Aichi,
JP), Yamaguchi; Takashi (Aichi, JP), Ozaki;
Nobutaka (Aichi, JP), Kanaya; Yasuhiro (Tokyo,
JP), Takeda; Hirohisa (Aichi, JP), Mikami;
Yasuo (Aichi, JP), Mutoh; Yoshifumi (Aichi,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Nagasawa; Koichi
Yamaguchi; Takashi
Ozaki; Nobutaka
Kanaya; Yasuhiro
Takeda; Hirohisa
Mikami; Yasuo
Mutoh; Yoshifumi |
Aichi
Aichi
Aichi
Tokyo
Aichi
Aichi
Aichi |
N/A
N/A
N/A
N/A
N/A
N/A
N/A |
JP
JP
JP
JP
JP
JP
JP |
|
|
Assignee: |
Japan Display West Inc. (Aichi,
JP)
|
Family
ID: |
40668961 |
Appl.
No.: |
12/849,675 |
Filed: |
August 3, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100314621 A1 |
Dec 16, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12275448 |
Nov 21, 2008 |
7838402 |
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Foreign Application Priority Data
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Nov 26, 2007 [JP] |
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2007-304357 |
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Current U.S.
Class: |
257/431; 257/359;
257/E21.077; 257/E21.058; 257/290; 257/E21.632; 257/E21.329;
257/E21.134; 257/E21.189; 257/E21.051; 257/E21.231; 257/E21.411;
257/E21.311 |
Current CPC
Class: |
H01L
27/1248 (20130101); G02F 1/133555 (20130101); G02F
1/13394 (20130101); H01L 29/78633 (20130101); G02F
1/136227 (20130101) |
Current International
Class: |
H01L
27/14 (20060101); H01L 31/00 (20060101) |
Field of
Search: |
;257/288,290,359,431,428,E21.051,E21.077,E21.058,E21.134,E21.189,E21.231,E21.311,E21.329,E21.411,E21.632 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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HEI 5-26189 |
|
Feb 1993 |
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JP |
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3356115 |
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Oct 2002 |
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JP |
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2004-309955 |
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Nov 2004 |
|
JP |
|
3642048 |
|
Feb 2005 |
|
JP |
|
Primary Examiner: Nhu; David
Attorney, Agent or Firm: Dentons US LLP
Parent Case Text
CROSS REFERENCES TO RELATED APPLICATIONS
This application is a division of U.S. patent application Ser. No.
12/275,448, filed Nov. 21, 2008, now U.S. Pat. No. 7,838,402, the
entirety of which is incorporated herein by reference to the extent
permitted by law. The present application claims priority to and
contains subject matter related to Japanese Patent Application JP
2007-304357 filed in the Japan Patent Office on Nov. 26, 2007, the
entire contents of which are incorporated herein by reference to
the extent permitted by law.
Claims
What is claimed is:
1. An apparatus comprising: a substrate with a bottom gate
p-channel type thin film transistor; a resist pattern over the
substrate; and a light shielding film operative to block light
having a wavelength shorter than 260 nm over at least a channel
part of said bottom gate p-channel type thin film transistor.
2. The apparatus of claim 1, wherein said resist pattern contains a
material which absorbs light having a wavelength of shorter than
260 nm, and is configured as said light shielding film of which the
thickness at least over said channel part of said bottom gate
p-channel type thin film transistor is so set as to block light
having a wavelength of shorter than 260 nm.
3. The apparatus of claim 1, wherein said light shielding film is
between said channel part of said bottom gate p-channel type thin
film transistor and said resist pattern.
4. The apparatus of claim 1, wherein: said resist pattern has a
plurality of contact holes; said substrate includes a display
region with a plurality of pixel electrodes connected to said
bottom gate p-channel type thin film transistor through said
contact holes and arranged in an array over said resist pattern,
and a peripheral region arranged in the periphery of said display
region; and said bottom gate p-channel type thin film transistor is
in said peripheral region.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing an
electronic apparatus, and an electronic apparatus. More
particularly, the invention relates to a method of manufacturing an
electronic apparatus, and an electronic apparatus, in which a
resist pattern is provided as an insulating film over a substrate
provided with thin film transistors, such as a display device.
In a thin type electronic apparatus such as a liquid crystal
display device, for example, an electronic circuit such as a pixel
circuit and a driving circuit which uses a plurality of thin film
transistors is provided on a substrate. In such an electronic
apparatus, a resist pattern is used as an inter-layer insulating
film covering the thin film transistors. In a liquid crystal
display device, for example, a positive-type resist material
containing a highly transparent acrylic polymer as a base resin and
a diazo compound as a photosensitive agent is used.
The resist pattern is formed as follows. First, an uncured resist
film is formed on a substrate by application, and the uncured
resist film is subjected to an exposing and developing treatment to
form a resist pattern. Thereafter, further, the resist pattern is
heat cured. In the heat curing, for example, in the case of the
above-mentioned positive-type resist containing a diazo compound as
a photosensitive agent, irradiation with ultraviolet light having a
wavelength of up to 320 nm leads to a remarkable shortening of the
treating time (refer to Japanese Patent Publication No. Hei
5-26189).
In addition, as a means for enhancing the heat resistant of the
resist film after heating curing, for example, a method in which
irradiation with light containing ultraviolet rays is conducted at
the time of heat curing has been proposed (refer to Japanese Patent
No. 3356115). Further, a method in which irradiation with a high
energy radiation is conducted under a reduced pressure and then
heat curing is conducted has been proposed. It is said that,
according to this procedure, a cross-linking reaction proceeds
while conversion of the diazo compound as the photosensitive agent
into a carboxylic acid is prevented, so that a resist pattern which
is dense and shows enhanced heat resistance and chemical resistance
is obtained (refer to Japanese Patent Laid-open No.
2004-309955).
SUMMARY OF THE INVENTION
It has been found, however, that in the above-mentioned
manufacturing method, irradiation of channel parts of the thin film
transistors with ultraviolet light during the curing treatment of
the resist pattern causes degradation of characteristics of the
thin film transistors, particularly, p-channel type thin film
transistors, as shown in FIG. 25. Besides, as shown in FIG. 26, the
degradation of characteristics of the thin film transistors becomes
heavier as the irradiation energy is higher, as compared with the
characteristics obtained without irradiation with ultraviolet
light.
Thus, there is a need for a method of manufacturing an electronic
apparatus, and an electronic apparatus, in which a resist pattern
can be cured while maintaining its shape immediately upon
lithography, without degrading the characteristics of thin film
transistors covered with the resist pattern.
In accordance with one embodiment of the present invention, there
is provided a method of manufacturing an electronic apparatus
having a resist pattern provided over a substrate provided with
thin film transistors, the method being carried out as follows.
First, a resist film is formed by application over the substrate in
the condition of covering the thin film transistors. Next, the
resist film is subjected to exposing and developing treatments,
thereby forming the resist pattern. Thereafter, the substrate
provided with the resist pattern is subjected to a drying
treatment. Subsequently, the resist pattern having undergone the
drying treatment is irradiated with at least one of ultraviolet
light and visible light in a dry atmosphere. In this instance, the
irradiation with light is conducted in the condition where channel
parts of the thin film transistors are prevented from being
irradiated with light having a wavelength of shorter than 260 nm.
Thereafter, the resist pattern is heat cured.
In the method as above-mentioned, before the step of heat curing
the resist pattern patterned through the exposure and development,
a step of irradiating with at least one of ultraviolet light and
visible light in an atmosphere filled with a dry gas is carried
out. This ensures that reflow of the resist material during the
subsequent heat curing is prevented, and the surface shape of the
resist pattern is maintained in the shape as patterned through the
exposure and development. Further, in the step of irradiating with
at least one of ultraviolet light and visible light, the channel
parts of the thin film transistors are prevented from being
irradiated with light having a wavelength of shorter than 260 nm.
Therefore, degradation of characteristics of the thin film
transistors, particularly, degradation of characteristics of p-type
thin film transistors p-Tr, can be prevented from occurring due to
irradiation of the channel parts with short-wavelength light.
Besides, in accordance with another embodiment of the present
invention, there is provided a configuration of an electronic
apparatus suitable for the above-mentioned manufacturing method
according to the one embodiment of the present invention. In the
electronic apparatus, the thin film transistors are of a bottom
gate type, and a light shielding film operative to cut off
irradiation with light having a wavelength of shorter than 260 nm
is provided at least over the channel parts of the thin film
transistors of p-channel type.
According to the embodiments of the present invention as
above-mentioned, it is possible to obtain a liquid crystal display
device 36 having a highly heat-resistant resist pattern cured
assuredly while maintaining its shape immediately upon lithography,
without degradation of characteristics of thin film transistors
covered with the resist pattern.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A to 1C are sectional step views for illustrating
manufacturing methods according to first to fourth embodiments;
FIG. 2 is a flowchart illustrating a prime part of the
manufacturing method according to the first embodiment;
FIG. 3 is an essential part sectional view of a liquid crystal
display device obtained in the first to fourth embodiments;
FIGS. 4R, 4A and 4B show surface conditions of resist patterns
obtained according to the procedure and histories in the first
embodiment;
FIG. 5 shows the results of measurement of shape maintaining level
of resist patterns cured by changing the wavelength range of light
with which the resist pattern is irradiated in a curing treatment
within the range of the first embodiment;
FIGS. 6A and 6B are diagrams showing the transistor characteristics
of a thin film transistor beneath a resist pattern, after a curing
treatment of the resist pattern according to the procedure of the
first embodiment and after a comparative treatment;
FIG. 7 is a diagram showing the absorption spectra of resist
patterns obtained according to the procedure and histories in the
first embodiment;
FIG. 8 is a flowchart illustrating a prime part of the
manufacturing method according to the second embodiment;
FIG. 9 is a diagram showing the absorption spectrum, before
exposure to light, of a resist material used in the second
embodiment;
FIG. 10 is a diagram showing the transistor characteristics of a
thin film transistor beneath resist patterns, different in film
thickness, of the resist material showing the absorption spectrum
of FIG. 9;
FIG. 11 is a flowchart illustrating a prime part of the
manufacturing method according to the third embodiment;
FIG. 12 is an essential part sectional view illustrating a prime
part of the manufacturing method according to the third
embodiment;
FIG. 13 is a flowchart illustrating a prime part of the
manufacturing method according to the fourth embodiment;
FIG. 14 is a diagram showing the transistor characteristics of a
thin film transistor beneath a resist pattern cured by applying the
method according to the fourth embodiment, together with a
reference;
FIGS. 15A to 15C are sectional step views for illustrating a
manufacturing method according to a fifth embodiment;
FIG. 16 is a flowchart illustrating a prime part of the
manufacturing method according to the fifth embodiment;
FIG. 17 is an essential part sectional view of a liquid crystal
display device obtained in the fifth embodiment;
FIG. 18 is a diagram showing the transistor characteristics of a
thin film transistor beneath a resist pattern cured by applying the
method according to the fifth embodiment, together with a
reference;
FIG. 19 is a diagram showing an example of the circuit
configuration of a liquid crystal display device according to an
embodiment;
FIG. 20 is a perspective view of a TV set to which the present
invention is applied;
FIGS. 21A and 21B show a digital camera to which the present
invention is applied, wherein FIG. 21A is a perspective view from
the face side, and FIG. 21B is a perspective view from the back
side;
FIG. 22 is a perspective view of a notebook size personal computer
to which the present invention is applied;
FIG. 23 is a perspective view of a video camera to which the
present invention is applied;
FIGS. 24A to 24G show a PDA, for example, a mobile phone, to which
the present invention is applied, wherein FIG. 24A is a front view
of an opened state, FIG. 24B is a side view of the same, FIG. 24C
is a front view of a closed state, FIG. 24D is a left side view,
FIG. 24E is a right side view, FIG. 24F is a top view, and FIG. 24G
is a bottom view;
FIG. 25 is a diagram showing degradation of characteristics of a
p-channel type thin film transistor by irradiation with ultraviolet
light; and
FIG. 26 is a diagram showing degradation of characteristics of a
thin film transistor on the basis of irradiation energy of
ultraviolet light.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, embodiments in which the present invention is applied to a
method of manufacturing an active matrix driving type
semi-transmitting semi-reflecting liquid crystal display device, as
one of electronic apparatuses provided with thin film transistors,
will be described below.
First Embodiment
FIGS. 1A to 1C are sectional step views illustrating the
manufacturing method according to a first embodiment, showing a
one-pixel portion of a display region 1a of the liquid crystal
display device, and an essential part of a peripheral region 1b
arranged in the periphery of the display region 1a.
First, as shown in FIG. 1A, bottom gate type thin film transistors
Tr each having a gate electrode 3, a gate insulating film 5, and a
semiconductor layer 7 laminated sequentially are formed on a
transparent first substrate 1 made of a glass or the like. In this
case, for example in the display region 1a, an n-channel type thin
film transistor (n-type thin film transistor) n-Tr is formed
correspondingly to each pixel. In the peripheral region 1b, on the
other hand, an n-type thin film transistor n-Tr and a p-type thin
film transistor p-Tr are formed. Incidentally, in the peripheral
region 1b in the drawings, only the p-type thin film transistor
p-Tr is shown.
Next, the first substrate 1 provided with the thin film transistors
Tr is covered on the upper side with an inter-layer insulating film
9, and wirings 11 are formed which are connected to the thin film
transistors Tr through contact holes formed in the inter-layer
insulating film 9. As a result, each of pixels in the display
region 1a is provided with a pixel circuit 13 using the thin film
transistor Tr. In addition, in the peripheral region 1b, driving
circuits 15 of a CMOS configuration using the n-type thin film
transistor n-Tr and the p-type thin film transistor p-Tr are
formed. Details of the pixel circuit 13 and the driving circuit 15
will be described later.
In the above-mentioned manner, a so-called TFT substrate 20 is
formed. On the face side of the TFT substrate 20, a rugged shape
(projection-and-recess shape) due to the thin film transistors Tr
and the wirings 11 is generated.
Subsequently, as shown in FIG. 1B, an uncured resist film 22 is
formed on the TFT substrate 20 by application (coating). Here, a
positive-type resist containing a diazo compound as a
photosensitive agent and at least one of an acrylic ester and a
methacrylic ester as a base resin is used. Incidentally, as the
resist material, for example, the resist materials exemplified in
Japanese Patent No. 3642048 may be used. Further, it is desirable
that the resist material contains a compound having an epoxy group,
which permits the resist film to be cured easily.
Besides, here, the resist film 22 using such a resist material is
formed in a thickness of about 3.5 to 6.0 .mu.m. This ensures that
the rugged shape on the face side of the TFT substrate 20 is
sufficiently leveled off, and the structure composed of the resist
film 22 is formed in a sufficient height.
Next, the resist film 22 formed in the large thickness is subjected
to multi-step pattern exposure in which exposure is controlled.
Here, since the positive-type resist is used to form the resist
film 22, multi-step exposure is conducted in which light exposure
is controlled to be smaller in an area where the resist film 22 is
to be left in a larger thickness after a developing treatment.
For example, a contact part 22c just over the wiring 11 is
subjected to exposure in a largest light exposure for forming the
contact holes as through-holes by entirely removing the resist film
22 there. On the other hand, a spacer part 22s for forming a
columnar spacer for controlling the cell gap in the liquid crystal
display device is prevented from being irradiated with the exposure
light, whereby the resist film 22 is made to be left in a largest
thickness there. Besides, in the display region 1a, a transmitting
display part 1t is subjected to exposure in a larger light exposure
than a reflecting display part 1r, since the transmitting display
part 1t is to be so dug as to be lower in level than the reflecting
display part 1r, with a step therebetween. The reflecting display
part 1r is subjected to exposure for providing a light diffusing
surface having a rugged surface shape. Furthermore, the
transmitting display part 1t and the reflecting display part 1r are
subjected to exposure for providing recessed or projected orienting
elements for regulating the orientation of liquid crystal molecules
constituting a liquid crystal layer, as occasion demands.
Incidentally, in the first embodiment, it suffices to subject the
peripheral region 1b to exposure such that the resist film 22 will
be left in a requisite thickness.
In the exposure as above, it is important that of the thin film
transistors Tr, particularly, channel parts ch of the p-type thin
film transistors p-Tr are prevented from being irradiated with
light having a wavelength of shorter than 260 nm. Usually, such
exposure is conducted by use of a stepper having an extra-high
pressure mercury lamp as a light source. Bright lines of the
exposure light radiated from the extra-high pressure mercury lamp
are 365 nm (g line)/405 nm (h line)/436 nm (i line), and the
channel parts ch are not irradiated with light having a wavelength
of shorter than 260 nm. Therefore, the exposure here can be carried
out by applying the related-art exposure technology using a stepper
having the extra-high pressure mercury lamp.
After the multi-step exposure as above, the resist film 22 is
subjected to a developing treatment to perform patterning by which
the exposed parts are dissolved in a developing solution.
This produces a resist pattern 24 in which, as shown in FIG. 1C,
the resist film 22 is patterned into such a shape that a
predetermined step d to have the transmitting display part 1t at a
lower level and the reflecting display part 1r at an upper level is
provided, the reflecting display part 1r is provided with a light
diffusing surface 24b having a rugged shape, and a contact hole 24c
reaching the wiring 11 and a columnar spacer 24s are provided. In
addition, recessed or projected orienting elements are formed in a
patterned manner, as occasion demands.
Subsequently, steps for curing the resist pattern 24 are carried
out, which together with the subsequent steps constitute a prime
part of the first embodiment. Now, the curing process will be
described below using a flowchart shown in FIG. 2.
First, in step S1, the substrate provided with the resist pattern
as above-described is subjected to a drying treatment. This causes
removal of moisture (water) from the atmosphere surrounding the
resist pattern and from the resist film. The drying treatment is
carried out by reduced-pressure drying or by a combination of
reduced-pressure drying with heating drying. Incidentally, in the
case of the combination with heating drying, it is important to
prevent reflow of the resist material from occurring, by
maintaining the heating temperature below the glass transition
point of the resist material.
Here, the treating conditions used in the drying treatment step
become parameters for controlling the ruggedness of the surface
shape of the resist pattern after heat curing. Specifically, by
varying the reduced pressure value (degree of vacuum) and the
heating temperature as the treating conditions in the drying
treatment, the fluidity of the resist material at the time of heat
curing is controlled. This ensures that the ruggedness of the
surface shape of the resist pattern after the heat curing is
controlled within a range smaller than that immediately after the
developing treatment. In view of this, it is preferable that
treating conditions for bringing the ruggedness of the surface
shape of the resist pattern after heat curing into a predetermined
state are preliminarily detected, for example, by conducting a
preliminary experiment, and the drying treatment is carried out
under the treating conditions thus detected.
Next, in step S2-1, the resist pattern having undergone the drying
treatment is irradiated with light containing ultraviolet light in
a dry atmosphere filled with a dry gas. Especially, here, it is
important to conduct the irradiation in the condition where the
channel parts of the thin film transistors are prevented from being
irradiated with light having a wavelength of shorter than 260
nm.
Here, an inert gas such as nitrogen (N.sub.2), helium (He), argon
(Ar), etc. is used as the dry gas. Therefore, for example, a dry
gas with a dew point of not higher than -60.degree. C. is
preferably used; as an example, a nitrogen (N.sub.2) atmosphere
with a dew point of -60.degree. C. (moisture concentration: about
11 ppm) is used.
In addition, it is important to prevent volatilization (degassing)
of low molecular weight compounds from the resist pattern, and it
is preferable to maintain the pressure of the dry gas atmosphere at
around the atmospheric pressure. It is to be noted here that the
dry atmosphere may be a vacuum atmosphere or a reduced-pressure
atmosphere.
Incidentally, the moisture concentration in the treating atmosphere
is preferably kept at or below 4,000 ppm, but the moisture
concentration may be moderated to a certain extent depending on the
shape accuracy necessary for the resist pattern.
In addition, the light containing ultraviolet light with which the
resist pattern is irradiated preferably contains visible light
together with ultraviolet light, which is used for achieving the
subsequent heat curing of the resist pattern with a good shape
accuracy. As the visible light, light with a wavelength of 400 to
450 nm is preferably used.
In view of the above, in this first embodiment, a light source
which has bright lines in the ultraviolet and visible ranges and
which is suited to irradiation of a wide area with light is used as
the light source for irradiation with light. Examples of the light
source which can be used here include an high pressure mercury lamp
(bright lines: 254 nm/365 nm/405 nm/436 nm/546 nm/577 nm/579 nm)
and a low pressure mercury lamp (bright lines: 185 nm/254 nm/436
nm/550 nm).
Besides, especially, it is important to conduct the irradiation
with light in the condition where the channel parts of the thin
film transistors are prevented from being irradiated with light
having a wavelength of shorter than 260 nm. Therefore, the light
source is equipped with an optical filter for shielding the light
having a wavelength of shorter than 260 nm, and the resist pattern
is irradiated with light through the optical filter.
This ensures that the resist pattern is irradiated with light which
contains visible light together with ultraviolet light having a
wavelength of not less than 260 nm, and, in this instance, the
channel parts of the thin film transistors are prevented from being
irradiated with light having a wavelength of shorter than 260
nm.
Further, the step of the irradiation with light containing
ultraviolet light may be carried out under a heating condition. In
this case, it is possible to prevent reflow of the resist material
from occurring, by keeping the heating temperature below the glass
transition point of the resist material; for example, the
irradiation is carried out under heating at about 80.degree. C.
Here, the treating conditions in the step of irradiating with light
containing ultraviolet light become parameters for controlling the
ruggedness of the surface shape of the resist pattern after heat
curing. Specifically, by varying the light irradiation energy and
the heating temperature at the time of irradiation with light as
the treating conditions in the step of irradiating with light
containing ultraviolet light, the fluidity of the resist material
at the time of heat curing is controlled. This ensures that the
ruggedness of the surface shape of the resist pattern after the
heat curing is controlled within a range smaller than that
immediately after the developing treatment. Therefore, it is
preferable to preliminarily detect the treating conditions such as
to bring the ruggedness of the surface shape of the resist pattern
after heat curing into a predetermined state, for example, by
conducting a preliminary experiment, and to carry out the
irradiation with light containing ultraviolet light under the
treating conditions thus detected.
Thereafter, in step S3, a heat curing treatment of the resist
pattern is conducted. Here, heat curing at a heating temperature
according to the resist material constituting the resist pattern,
i.e., production burning, is conducted, whereby the resist pattern
having been patterned into a predetermined shape by the developing
treatment is securely cured. In such heat curing, production
burning at a heating temperature of generally 200 to 300.degree. C.
is carried out.
After the above, as shown in FIG. 3, pixel electrodes 26, 28 are
formed on the heat-cured resist pattern 24'. Of these pixel
electrodes 26, 28, the pixel electrode 26 in the transmitting
display part 1t is formed as a transparent electrode 26 formed of a
transparent electrode material such as ITO (Indium Tin Oxide). On
the other hand, the pixel electrode 28 in the reflecting display
part 1r is formed as a reflecting electrode 28 formed of a material
with good light reflecting characteristics such as aluminum. Here,
it is important for the reflecting electrode 28 to be formed in
conformity with the light diffusing surface 24b having a rugged
shape which is formed at the resist pattern 24. As a result, the
part of the resist pattern 24' formed with the light diffusing
surface 24b and the reflecting electrode 28 constitute a diffusing
reflective plate, and the surface of the reflecting electrode 28
constitutes a light diffusing reflective surface.
Incidentally, since the transparent electrode 26 and the reflecting
electrode 28 constitute a pixel electrode for one pixel, these
electrodes 26 and 28 are provided in the state of being connected
to each other. In addition, in order to prevent the pixel circuit
having the thin film transistor Tr from influencing the display,
the reflecting electrode 28 is provided at such a position as to
overlap with the pixel circuit. Besides, the transparent electrode
26 is connected to the wiring 11 through the contact hole 24c, and
this contact portion is covered with the reflecting electrode 28.
Further, the pixel electrodes 26, 28 are removed at the position of
the columnar spacer 24s.
After the pixel electrodes each composed of the transparent
electrode 26 and the reflecting electrode 28 are formed, an
orienting film (omitted in the drawing) covering these electrodes
is formed.
In addition, a second substrate 30 to be opposed to the first
substrate 1 provided with the structure on the upper side thereof
as above is prepared. The second substrate 30 is composed of a
transparent substrate made of a glass or the like, and is provided
with a counter electrode 32 formed in a solid film shape from a
transparent conductive material. Besides, an orienting film
(omitted in the drawing) is provided in the state of covering the
counter electrode 32. Incidentally, if occasion demands, the second
substrate 30 may be provided with a color filter (omitted in the
drawing here) formed in a patterned manner. The color filter is
provided beneath the counter electrode 32.
Next, the pixel electrodes 26, 28 formed on the side of the first
substrate 1 and the counter electrode 32 formed on the side of the
second substrate 30 are disposed opposite to each other, and the
columnar spacer 24s is clamped therebetween. In this condition, the
gap between the substrates 1 and 30 is filled with a liquid crystal
layer LC containing liquid crystal molecules m, to seal the gap
between the substrates 1 and 30.
In the above-mentioned manner, a liquid crystal display device 36
having the liquid crystal layer LC sandwiched between the two
substrates 1 and 30 is obtained. In the liquid crystal display
device 36, the resist pattern 24' covering the upper side of the
first substrate 1 buries the ruggedness on the upper side of the
first substrate 1, and it is formed as an integral structure
provided with a plurality of recessed and projected shapes in its
surface.
Specifically, the resist pattern 24' is securely heat cured, and
the step (d) and the columnar spacer 24s for partially controlling
the layer thickness of the liquid crystal layer LC (i.e., cell gaps
g1, g2) are integrally formed, together with the light diffusing
surface 24b with the rugged surface shape for diffusing display
light.
According to the first embodiment described above, the step of
irradiating with light containing ultraviolet light in an
atmosphere filled with a dry gas (step S2-1) is conducted before
the step of heat curing the resist pattern obtained by patterning
through exposure and development (step S3), as has been described
referring to FIG. 2. This ensures that reflow of the resist
material at the time of heat curing in step S3 is prevented, and
the surface shape of the resist pattern is maintained in the shape
obtained by patterning through exposure and development.
Therefore, the resist pattern in an enlarged thickness can be heat
cured in the condition where the rugged surface shape is
maintained.
Especially, in the step of irradiating with light containing
ultraviolet light (step S2-1), the light source is fitted with the
optical filter for shielding the light having a wavelength of
shorter than 260 nm, and the resist pattern is irradiated with
light through the optical filter. This ensures that, as shown in
FIG. 1C, the channel parts of the bottom gate type thin film
transistors Tr beneath the resist pattern 24 are prevented from
being irradiated with light having a wavelength of shorter than 260
nm, and degradation of characteristics of the thin film transistors
Tr, particularly, degradation of characteristics of the p-type thin
film transistors p-Tr, due to irradiation of the channel parts ch
with short-wavelength light can be prevented from occurring.
As a result, by the method according to the first embodiment, it is
possible to obtain a liquid crystal display device 36 having the
resist pattern 24' with good heat resistance which is securely
cured in the state of maintaining the shape immediately upon
lithography, without any degradation of characteristics of the thin
film transistors Tr covered with the resist pattern 24'.
FIGS. 4R, 4A and 4B show the surface states of resist patterns
having different histories. Each of the resist patterns was formed
by a method in which a resist film of a positive-type resist
containing a diazo compound as a photosensitive agent is formed by
application (coating), and is subjected to exposure and development
to form a light diffusing surface 24b having a rugged shape and a
contact hole 24c.
FIG. 4R shows a resist pattern immediately upon development,
wherein the shape accuracy of the light diffusing surface 24b and
the contact hole 24c is maintained.
FIG. 4A shows a resist pattern cured along the flowchart of FIG. 2
in the first embodiment. Here, first, reduced-pressure drying of a
resist pattern after development was conducted as step S1. Next, as
step S2-1, irradiation with light containing ultraviolet light was
conducted in a treating chamber filled with a nitrogen (N.sub.2)
atmosphere (dry gas atmosphere) with a moisture concentration of
not more than 50 ppm. In this case, a high pressure mercury lamp
was used as a light source, and irradiation with light was
conducted through an optical filter operative to absorb not less
than 99% of ultraviolet light having a wavelength of not more than
300 nm. In addition, the substrate was heated to a temperature of
80 to 100.degree. C. Thereafter, as step S3, a heat curing
treatment at 220.degree. C. was conducted.
FIG. 4B shows a resist pattern cured without applying the first
embodiment. Here, first, a resist pattern after development was
irradiated with light by using an extra-high pressure mercury lamp
as a light source, without being subjected to any drying treatment.
Since the light from the extra-high pressure mercury lamp does not
contain light having a wavelength of shorter than 260 nm, the same
irradiation with light as that used in step S2-1 was practically
carried out as a pre-treatment for the heat curing treatment.
Thereafter, a heat curing treatment was conducted at 220.degree.
C.
By comparing these resist patterns, it could be confirmed that the
resist pattern [FIG. 4A] heat cured according to the procedure of
the first embodiment retains the rugged surface shape of the resist
pattern [FIG. 4R] immediately after the developing treatment. On
the other hand, the resist pattern [FIG. 4B] irradiated with light
and heat cured, without being subjected to the drying treatment of
step S1 in the first embodiment and without being subjected to the
treating atmosphere and temperature control of step S2, showed
reflow of the resist material at the time of heat curing, and could
not retain its shape after development.
In addition, FIG. 5 shows the results of measurement, at four
locations, of the level of retention of the resist pattern shape
immediately upon development, for resist patterns cured by varying
the wavelength range of the light used for irradiation in step S2-1
within the range of the first embodiment, in the resist pattern
curing treatment. A high pressure mercury lamp (bright lines: 254
nm/365 nm/405 nm/436 nm/546 nm/577 nm/579 nm) was used as the light
source, and the wavelength range of irradiation of the resist
pattern was controlled by an optical filter.
FIG. 5, (A)-1, shows the case of irradiation with light from which
light component having a wavelength of not more than 300 nm was cut
off by an optical filter and which had main wavelengths of 365
nm/405 nm/436 nm/546 nm/577 nm/579 nm.
FIG. 5, (A)-2, shows the case of irradiation with light in which
light component having a wavelength of 300 to 375 nm was
transmitted through an optical filter and which had a main
wavelength of 365 nm.
From the results shown in FIG. 5, it is seen that the resist
pattern [FIG. 5, (A)-1] irradiated with visible light having a
wavelength of not less than 400 nm in addition to ultraviolet light
can retain the shape upon development more favorably and is higher
in heat resistance, than the resist pattern [FIG. 5, (A)-2]
irradiated only with ultraviolet light having a main wavelength of
365 nm. By this, the effect of irradiating with visible light in
addition to ultraviolet light in step S2-1 before the heat curing
treatment was confirmed.
This is interpreted as follows. In an ordinary ultraviolet curing
process, it is aimed at enhancing heat resistance by breaking bonds
in the resist in question and then effecting re-bonding. On the
other hand, the light in the visible region of a wavelength of not
less than 400 nm has only low energy of about 250 to 300 kJ/mol,
and may not break the bonds. However, in the irradiation with light
in a dry atmosphere described in the first embodiment above (step
S2-1), the resist pattern is irradiated with light in the visible
region of a wavelength of not less than 400 nm, whereby an
intermediate produced upon sensitizing (exposure) of the
positive-type resist can be brought into a cross-linking reaction.
As a result, in the irradiation with light in a dry atmosphere
(step S2-1), the resist pattern is irradiated with light in the
visible region in addition to ultraviolet light, whereby the heat
resistance of the resist pattern can be enhanced effectively.
FIGS. 6A and 6B show, as transistor characteristic, the
relationship between gate voltage and drain current of a p-type
thin film transistor, after a curing treatment of a resist pattern
formed on the bottom gate type thin film transistor.
FIG. 6A shows the transistor characteristic of the thin film
transistor beneath the resist pattern cured by applying the method
according to the first embodiment [HIGH PRESSURE MERCURY LAMP (WITH
OPTICAL FILTER)]. In step S2-1, the resist pattern was irradiated
with the light from a high pressure mercury lamp through an optical
filter for shielding the light having a wavelength of shorter than
260 nm, and thereafter the heat curing treatment in step S3 was
conducted. Besides, the transistor characteristic before
irradiation with light [UNIRRADIATED (REFERENCE)] is shown
together.
FIG. 6B shows the transistor characteristic of the thin film
transistor beneath the resist pattern cured without applying the
method according to the first embodiment [HIGH PRESSURE MERCURY
LAMP (WITHOUT OPTICAL FILTER)]. In step S2-1, the resist pattern
was irradiated with the light from a high pressure mercury lamp
containing light having a wavelength of shorter than 260 nm, and
thereafter the heat curing treatment in step S3 was conducted.
Besides, the transistor characteristic before irradiation with
light [UNIRRADIATED (REFERENCE)] is shown together.
By comparing these transistor characteristics, it was confirmed
that the characteristic of the thin film transistor beneath the
resist pattern heat cured in the procedure of the first embodiment
[FIG. 6A] retained the characteristic before irradiation with light
[UNIRRADIATED (REFERENCE)] and was free of degradation. On the
other hand, the characteristic of the thin film transistor beneath
the resist pattern formed without applying the first embodiment,
specifically, the resist pattern irradiated with the light having a
wavelength of shorter than 260 nm before the heat curing treatment
[FIG. 6B] was confirmed to show a degradation, specifically, a
shifting of threshold voltage, as compared with the characteristic
before irradiation with light [UNIRRADIATED (REFERENCE)].
In addition, FIG. 7 shows absorption spectra of resist patterns
having different histories. In the diagram, (R) is the absorption
spectrum of a resist pattern immediately upon development; (A) is
the absorption spectrum of a resist pattern cured along the
flowchart of FIG. 2 in the first embodiment; and (B) is the
absorption spectrum of a resist pattern formed without applying the
first embodiment, specifically, a resist pattern formed by a heat
curing treatment after irradiation with ultraviolet light having a
wavelength of 250 nm.
Based on the comparison of these absorption spectra, in the first
embodiment, the resist pattern is irradiated with visible light in
addition to ultraviolet light in step S2-1. Therefore, the resist
pattern is irradiated with light having a wavelength in the range
of 270 to 600 n, hitherto used in a decoloring treatment of a
positive-type resist, whereby a decoloring effect can also be
obtained. As a result, for example in the transmitting display part
1t shown in FIG. 3, enhancement of luminance (brightness) of the
display light can be promised, without performing any special
decoloring step.
Second Embodiment
A second embodiment is assumed to differ from the first embodiment
in that the resist pattern itself is used as a light shielding film
for channel parts of thin film transistors in irradiating the
resist pattern with light as a preliminary step for a heat curing
treatment of the resist pattern.
In this case, the step described referring to FIG. 1C in the first
embodiment above is conducted in the same manner as above, to form
circuits using thin film transistors in the display region 1a and
the peripheral region 1b on the first substrate 1, thereby
obtaining a TFT substrate 20.
Next, as shown in FIG. 1B, an uncured resist film 22 is formed on
the TFT substrate 20 by application (coating). In this case, an
acrylic positive-type photoresist or a cresol-novolak resin
photoresist showing great light absorption on the short wavelength
side is used. In addition, here, multi-step exposure such that the
light exposure is controlled to be smaller in an area where the
resist film 22 is to be left in a larger thickness after a
developing treatment, as described in the first embodiment above,
is conducted. Therefore, it is preferable to use the acrylic
positive-type photoresist which is the same as or similar to that
in the first embodiment.
Besides, in this second embodiment, it is important to apply the
resist film 2 in a sufficient thickness so that a resist pattern in
a sufficient film thickness will be formed after the developing
treatment, in the region where p-type thin film transistors p-Tr
are provided, i.e., in the peripheral region 1b. The requisite film
thickness of the resist pattern formed in the peripheral region 1b
depends on the composition of the resist material, and is assumed
to be such a thickness as to be able to shield, by absorbing, the
light having a wavelength of shorter than 260 nm.
Thereafter, the resist film 22 formed by applying in a large
thickness is subjected to multi-step pattern exposure in which the
light exposure is controlled in the same manner as in the first
embodiment. It is to be noted here, however, that in the second
embodiment the exposure is not needed for at least those portions
of the resist film 22 which are located on the upper side of the
p-type thin film transistors p-Tr in the peripheral region 1b.
In the exposure as above, like in the first embodiment, it is
important that particularly the channel parts ch of the p-type thin
film transistors p-Tr, of the thin film transistors Tr, are
prevented from being irradiated with light having a wavelength of
shorter than 260 nm. Therefore, like in the first embodiment, the
exposure can be carried out by applying the related-art exposure
technology using a stepper having an extra-high pressure mercury
lamp as a light source.
After the multi-step exposure as above, the resist film 22 is
subjected to a developing treatment, so as to dissolve the exposed
portions into a developing solution, thereby patterning the resist
film 22.
Consequently, as shown in FIG. 1C, it is possible to obtain a
resist pattern 24 by patterning the resist film 22 into such a
shape that a predetermined step d for having a transmitting display
part 1t at a lower level and a reflecting display part 1r at an
upper level is provided, the reflecting display part 1r is provided
with a light diffusing surface 24b having a rugged shape, and a
contact hole 24c reaching a wiring 11 and a columnar spacer 24s are
provided. In addition, if occasion demands, recessed or projected
orienting elements are formed in a patterned manner. Especially, at
least on the p-type thin film transistors p-Tr in the peripheral
region 1b, a resist pattern 24 is formed in such a thickness as to
be able to shield, by absorbing, the light having a wavelength of
shorter than 260 nm.
The next and subsequent steps constitute a process of curing the
resist pattern 24. Now, the curing process will be described below
using a flowchart shown in FIG. 8. In this second embodiment, step
S2-2 is a prime part, whereas steps S1 and S3 may be the same as in
the first embodiment, and description thereof is omitted here.
First, in step S1, the substrate provided with the resist pattern
is subjected to a drying treatment. Thereafter, in step S2-2, the
resist pattern having undergone the drying treatment is irradiated
with light containing ultraviolet light in an atmosphere filled
with a dry gas. In this case, like in the first embodiment, the
irradiation with light is conducted in the condition where the
channel parts of the thin film transistors are prevented from being
irradiated with light having a wavelength of shorter than 260 nm.
In the second embodiment, the shielding of the light having a
wavelength of shorter than 260 nm is performed by the resist
pattern, and the other configurations are the same as in step S2-1
of the first embodiment.
Specifically, as the dry gas, an inert gas is used in the same
manner as in the first embodiment.
In addition, as the light containing ultraviolet light with which
the resist pattern is irradiated, visible light is used together
with the ultraviolet light, which is used to perform the subsequent
heat curing of the resist pattern with a good shape accuracy, like
in the first embodiment. Therefore, as the light source for
irradiation with light, a light source which has bright lines in
the ultraviolet and visible ranges and which is suited to
irradiation of a wide area with light is used. Examples of the
light source for use here include a high pressure mercury lamp
(bright lines: 254 nm/365 nm/405 nm/436 nm/546 nm/577 nm/579 nm)
and a low pressure mercury lamp (bright lines: 185 nm/254 nm/436
nm/550 nm).
Besides, the resist pattern is irradiated with light containing
visible light together with ultraviolet light, whereby the resist
pattern formed in a sufficient film thickness particularly in the
peripheral region is permitted to function as a light shielding
film, so that the channel parts of the p-type thin film transistors
are prevented from being irradiated with light having a wavelength
of shorter than 260 nm.
Incidentally, like in the first embodiment, the step of irradiating
with light containing ultraviolet light may be conducted in a
heating condition. In addition, the treating conditions in the step
of irradiation with the light containing ultraviolet light become
parameters for controlling the ruggedness of the surface shape of
the resist pattern after heat curing, in the same manner as above.
Therefore, like in the first embodiment, it is preferable to
preliminarily detect the treating conditions such as to bring the
ruggedness of the surface shape of the resist pattern after heat
curing into a predetermined state, for example, by conducting a
preliminary experiment, and to conduct the irradiation of the
resist pattern with the light containing ultraviolet light under
the treating conditions thus detected.
Thereafter, in step S3, a heat curing treatment of the resist
pattern is conducted, in the same manner as in the first
embodiment.
Further, after the above, a liquid crystal display device 36 having
a liquid crystal layer LC sandwiched between two substrates 1 and
30 is obtained, in the same manner as described referring to FIG. 3
in the first embodiment above.
In the liquid crystal display device 36, a resist pattern 24'
covering the upper side of the first substrate 1 is formed as an
integral structure which buries the ruggedness on the upper side of
the first substrate 1 and which is provided with a plurality of
recessed and projected shapes at the surface thereof.
According to the second embodiment as above, as has been described
referring to FIG. 8, a step of irradiating with light containing
ultraviolet light in an atmosphere filled with a dry gas (step
S2-2) is conducted before the step of heat curing the resist
pattern obtained by patterning through exposure and development.
This ensures that reflow of the resist material at the time of heat
curing in step S3 is prevented from occurring, and the surface
shape of the resist pattern is maintained in the shape obtained by
patterning through exposure and development.
Therefore, like in the first embodiment, the resist pattern formed
in an enlarged thickness can be heat cured in the state of
retaining the rugged surface shape thereof.
Particularly, in the step of irradiating with light containing
ultraviolet light (step S2-2), the resist pattern formed in a
sufficient film thickness in the peripheral region where the p-type
thin film transistors are provided is used as a light shielding
film for the light having a wavelength of shorter than 260 nm. This
ensures that, as shown in FIG. 1C, the channel parts of the bottom
gate type thin film transistors Tr provided in the peripheral
region 1b can be prevented from being irradiated with light having
a wavelength of shorter than 260 nm, and degradation of
characteristics of the p-type thin film transistors p-Tr due to
irradiation of the channel parts ch with short-wavelength light can
be prevented from occurring.
Consequently, by the method according to this second embodiment, it
is possible to obtain a liquid crystal display device 36 having a
resist pattern 24' with good heat resistance which is securely
cured in the state of retaining its shape immediately upon
lithography, without any degradation of characteristics of the thin
film transistors Tr covered with the resist pattern 24'.
Here, FIG. 9 shows an absorption spectrum before exposure, for a
resist material (acrylic positive-type photoresist) used in the
second embodiment. As shown in this diagram, it is important in the
second embodiment to use a resist material showing a high
absorption coefficient on the shorter wavelength side as compared
with 260 nm.
FIG. 10 shows transistor characteristic (relationship between gate
voltage and drain current) in the case where resist patterns using
the resist material showing the absorption spectrum of FIG. 9 were
formed in different film thicknesses on a bottom gate type p-type
thin film transistor, and were irradiated with 2000 mJ/cm.sup.2 of
light having a wavelength of 250 nm. Besides, transistor
characteristic in the case where the resist pattern was not
irradiated with the light having a wavelength of 250 nm was shown
as a reference.
From FIG. 10 it is seen that when a resist material having a light
absorption on the shorter wavelength side as compared with 260 nm
is used, it is possible to suppress the shifting of the threshold
value of the p-type thin film transistor due to irradiation with
light on the shorter wavelength side as compared with 260 nm (light
having a wavelength of 250 nm), by forming the resist pattern in an
enlarged film thickness. As an example, it was confirmed that in
the case of irradiation with 2000 mJ/cm.sup.2 of light having a
wavelength of 250 nm, it is possible to perfectly preventing the
shifting of the threshold value of the p-type thin film transistor,
by forming the resist pattern in a large film thickness of about
4.0 .mu.m.
Then, it is seen that it suffices for the film thickness of the
resist pattern formed on the channel parts of the p-type thin film
transistors to be set at such a value as to make it possible to
prevent the shifting of the threshold value of the p-type thin film
transistor by the energy of the light used for irradiation in step
S2-2.
Besides, in view of the fact that the resist pattern serves as the
light shielding film for the channel parts of the thin film
transistors as above-mentioned, even when exposure light containing
a wavelength shorter than 260 nm is used for pattern exposure in
applying lithography to the resist film, degradation of
characteristics of the thin film transistors due to the exposure
light can be prevented from occurring.
Third Embodiment
A third embodiment is assumed to differ from the first embodiment
in that a gate electrode is used as a light shielding film for a
channel part of a thin film transistor in conducting irradiation of
a resist pattern with light as a preliminary step for a heat curing
treatment of the resist pattern.
First, in the third embodiment, the steps shown in FIGS. 1A to 1C
are conducted in the same manner as described in the first
embodiment above, to form bottom gate type thin film transistors Tr
on a first substrate 1 and to form a resist pattern 24 covering
them.
Next, a step of curing the resist pattern 24 is carried out as
shown in a flowchart in FIG. 11. In this third embodiment, step
S2-3 is characteristic, whereas steps S1 and S3 may be the same as
in the first embodiment, and description thereof is omitted
here.
First, in step S1, the substrate provided with the resist pattern
is subjected to a drying treatment. Thereafter, in step S2-3, the
resist pattern having undergone the drying treatment is irradiated
with light containing ultraviolet light in an atmosphere filled
with a dry gas. In this case, like in the first embodiment, the
irradiation is conducted in the condition where the channel parts
of the thin film transistors are prevented from being irradiated
with light having a wavelength of shorter than 260 nm. In this
third embodiment, the shielding of the light having a wavelength of
shorter than 260 nm is conducted by the gate electrode, and the
other configurations are the same as in step S2-1 of the first
embodiment.
Specifically, as the dry gas, an inert gas is used in the same
manner as in the first embodiment.
In addition, like in the first embodiment, as the light containing
ultraviolet light with which the resist pattern is to be
irradiated, visible light for enhancing the light transmittance of
the heat-cured resist pattern is preferably used together with
ultraviolet light, which is used for conducting the subsequent heat
curing of the resist pattern with good shape accuracy. Therefore,
as a light source for irradiation with light, a light source which
has bright lines in the ultraviolet and visible ranges and which is
suited to irradiation of a wide area with light is used. Examples
of the light source for use here include a high pressure mercury
lamp (bright lines: 254 nm/365 nm/405 nm/436 nm/546 nm/577 nm/579
nm) and a low pressure mercury lamp (bright lines: 185 nm/254
nm/436 nm/530 nm).
Especially, in this third embodiment, as shown in FIG. 12,
irradiation with the above-mentioned light h containing ultraviolet
light is conducted from the back side of the first substrate 1.
This ensures that, in each of the thin film transistors Tr, the
gate electrode 3 serves as a light shielding film for the channel
part ch of a semiconductor layer 7, whereby irradiation of the
channel part ch with the light h is prevented. Thus, the channel
parts ch of the p-type thin film transistors p-Tr formed in the
peripheral region 1b are prevented from being irradiated with light
having a wavelength of shorter than 260 nm.
Incidentally, the step of irradiating with the light containing
ultraviolet light may be conducted under a heating condition, like
in the first embodiment. Besides, the treating conditions in the
step of irradiating with the light containing ultraviolet light
become parameters for controlling the ruggedness of the surface
shape of the resist pattern after heat curing, in the same manner
as above. Therefore, like in the first embodiment, it is preferable
to preliminarily detect the treating conditions such as to bring
the ruggedness of the surface shape of the resist pattern after
heat curing, for example, by conducting a preliminary experiment,
and to perform the irradiation with light containing ultraviolet
light under the treating conditions thus detected.
Thereafter, in step S3, a heat curing treatment of the resist
pattern is conducted, in the same manner as in the first
embodiment.
Further, after the above, a liquid crystal display device 36 having
a liquid crystal layer LC sandwiched between two substrates 1 and
30 is obtained, in the same manner as described referring to FIG. 3
in the first embodiment above.
In the liquid crystal display device 36, a resist pattern 24'
covering the upper side of the first substrate 1 is formed as an
integral structure which buries the ruggedness on the upper side of
the first substrate 1 and which is provided with a plurality of
recessed and projected shapes at its surface.
According to the third embodiment as above, as has been described
referring to FIGS. 11 and 12, the step of irradiating with light
containing ultraviolet light in an atmosphere filled with a dry gas
(step S2-3) is conducted before the step of heat curing the resist
pattern obtained by patterning through exposure and development
(step S3). This ensures that reflow of the resist material at the
time of heat curing in step S3 is prevented from occurring, and the
surface shape of the resist pattern is maintained in the shape
obtained by patterning through exposure and development.
Therefore, like in the first embodiment, the resist pattern formed
in an enlarged film thickness can be heat cured in the state of
retaining the rugged surface shape.
Particularly, in the step of irradiating with light containing
ultraviolet light (step S2-3), as shown in FIG. 12, irradiation
with the light h containing ultraviolet light is conducted from the
back side of the first substrate 1 while using the gate electrodes
as a light shielding film, whereby the channel parts ch of the
bottom gate type thin film transistors Tr are prevented from being
irradiated with light having a wavelength of shorter than 260 nm.
By this, it is possible to prevent degradation of characteristics
of the p-type thin film transistors p-Tr due to irradiation of the
channel parts ch with short-wavelength light.
Consequently, by the method according to the third embodiment, it
is possible to obtain a liquid crystal display device 36 having the
resist pattern 24' with good heat resistance which is securely
cured in the state of retaining its shape immediately upon
lithography, without any degradation of characteristics of the thin
film transistors Tr covered with the resist pattern 24'.
Fourth Embodiment
A fourth embodiment is assumed to differ from the first embodiment
in that a light source generating only light having a wavelength of
not less than 260 nm is used at the time of performing irradiation
of a resist pattern with light as a preliminary step for a heat
curing treatment of the resist pattern.
First, in this fourth embodiment, the steps shown in FIGS. 1A to 1C
are carried out in the same manner as described in the first
embodiment, to form bottom gate type thin film transistors Tr on a
first substrate 1, and to form a resist pattern 24 covering
them.
Next, a step of curing the resist pattern 24 is conducted as shown
in a flowchart in FIG. 13. In this fourth embodiment, step S2-4 is
a prime, whereas steps S1 and S3 may be the same as in the first
embodiment, so that description thereof is omitted here.
First, in step S1, the substrate provided with the resist pattern
is subjected to a drying treatment. Thereafter, in step S2-3, the
resist pattern having undergone the drying treatment is irradiated
with light containing ultraviolet light in an atmosphere filled
with a dry gas. In this case, like in the first embodiment, the
irradiation is conducted in the condition where the channel parts
of the thin film transistors are prevented from being irradiated
with light having a wavelength of shorter than 260 nm. In the
fourth embodiment, a light source generating only light having a
wavelength of not less than 260 nm is used as a light source for
supplying light containing ultraviolet light, and the other
configurations are the same as in step S2-1 of the first
embodiment.
Specifically, as the dry gas, an inert gas is used in the same
manner as in the first embodiment.
In addition, as the light containing ultraviolet light with which
to irradiate the resist pattern, like in the first embodiment,
visible light for enhancing the light transmittance of the
heat-cured resist pattern is preferably used together with
ultraviolet light, which is used for performing the subsequent heat
curing of the resist pattern with good shape accuracy. Therefore,
here, a light source which generates only light with a wavelength
of not less than 260 nm and which has bright lines in the
ultraviolet and visible ranges is used as the light source for
irradiation with light. For example, an extra-high pressure mercury
lamp (bright lines: 365 nm/405 nm/436 nm) is used.
It should be noted here that the extra-high pressure mercury lamp
is a point-like source of light. Therefore, in order to effectively
irradiate a wide area of the first substrate 1 with the light
containing ultraviolet light having a wavelength of not less than
260 nm, a mirror and/or a lens is provided for the light source, so
as to widen the irradiation light into a line-like form or a
plane-like form.
Incidentally, like in the first embodiment, the step of irradiating
with the light containing ultraviolet light may be conducted under
a heating condition. Besides, the treating conditions in the step
of irradiating with the light containing ultraviolet light become
parameters for controlling the ruggedness of the surface shape of
the resist pattern after heat curing, in the same manner as above.
Therefore, like in the first embodiment, it is preferable to
preliminarily detect the treating conditions such as to bring the
ruggedness of the surface shape of the resist pattern after heat
curing into a predetermined state, and to perform the irradiation
with the light containing ultraviolet light under the treating
conditions thus detected.
Thereafter, in step S3, like in the first embodiment, a heat curing
treatment of the resist pattern is conducted.
Further, after the above, a liquid crystal display device 36 having
a liquid crystal layer LC sandwiched between two substrates 1 and
30 is obtained, in the same manner as described referring to FIG. 3
in the first embodiment above.
In the liquid crystal display device 36, a resist pattern 24'
covering the first substrate 1 is formed as an integral structure
which buries the ruggedness on the upper side of the first
substrate 1 and which is provided with a plurality of recessed and
projected shapes at its surface.
According to the fourth embodiment as above-described, as has been
described referring to FIG. 13, the step of irradiating with light
containing ultraviolet light in an atmosphere filled with a dry gas
(step S2-4) is conducted before the step of heat curing the resist
pattern obtained by patterning through exposure and development
(step S3). This ensures that reflow of the resist material at the
time of heat curing in step S3 is prevented from occurring, and the
surface shape of the resist pattern is maintained in the shape
obtained by patterning through exposure and development.
Therefore, like in the first embodiment, the resist pattern formed
in an enlarged film thickness can be heat cured in the state of
retaining the rugged surface shape.
Particularly, in the step of irradiating with the light containing
ultraviolet light (step S2-4), the resist pattern is irradiated
with light by using a light source which generates only light in a
wavelength range of not less than 260 nm and which has bright lines
in the ultraviolet and visible ranges, such as an extra-high
pressure mercury lamp (bright lines: 365 nm/405 nm/436 nm). This
ensures that, as shown in FIG. 1C, the channel parts of the bottom
gate type thin film transistors Tr beneath the resist pattern 24
can be prevented from being irradiated with light having a
wavelength of shorter than 260 nm, and degradation of
characteristics of the thin film transistors Tr, specifically,
degradation of characteristics of the p-type thin film transistors
p-Tr, due to irradiation of the channel parts ch with
short-wavelength light, can be prevented from occurring.
Consequently, by the method according to the fourth embodiment, it
is possible to obtain a liquid crystal display device 36 having the
resist pattern 24' with good heat resistance which is securely
cured in the state of retaining its shape immediately upon
lithography, without any degradation of characteristics of the thin
film transistors Tr covered with the resist pattern 24'.
Here, FIG. 14 shows transistor characteristic of the thin film
transistors beneath the resist pattern cured by applying the method
of the fourth embodiment [IRRADIATION WITH LIGHT FROM EXTRA-HIGH
PRESSURE MERCURY LAMP]. In this case, the resist pattern was
irradiated with light from an extra-high pressure mercury lamp in
step S2-4, and, thereafter, the heat curing treatment in step S3
was carried out. Besides, transistor characteristic before
irradiation with light [UNIRRADIATED (REFERENCE)] is shown
together.
As shown in FIG. 14, the characteristic of the thin film
transistors beneath the resist pattern cured by applying the fourth
embodiment using the light source (extra-high pressure mercury
lamp) not generating the light having a wavelength of shorter than
260 nm was confirmed to be retaining the characteristic before
irradiation with light [UNIRRADIATED (REFERENCE)] and be free of
degradation.
Fifth Embodiment
A fifth embodiment differs from the first embodiment in that a
light shielding film is provided on the upper side of channel
parts, whereby irradiation of the channel parts with light having a
wavelength of shorter than 260 nm is prevented by the light
shielding film, at the time of performing irradiation of the resist
pattern with light as a preliminary step for a heat curing
treatment. Now, a manufacturing method according to the fifth
embodiment will be described below.
First, as shown in FIG. 15A, bottom gate type thin film transistors
Tr are formed on a first substrate 1 made of a transparent material
such as a glass. In this case, like in the first embodiment, for
example, n-type thin film transistors n-Tr are formed in a display
region 1a, each correspondingly to each pixel, whereas n-type thin
film transistors n-Tr and p-type thin film transistors p-Tr are
formed in a peripheral region 1b.
Next, the upper side of the first substrate 1 provided with the
thin film transistors Tr is covered with an inter-layer insulating
film 9, and wirings 11 connected to the thin film transistors Tr
through contact holes formed in the inter-layer insulating film 9
are formed. As a result, pixel circuits 13 using the thin film
transistors Tr are formed, one for each pixel in the display region
1a. Besides, in the peripheral region 1b, driving circuits 15 of a
CMOS configuration using the n-type thin film transistor n-Tr and
the p-type thin film transistor p-Tr are formed.
In this case, particularly in the fifth embodiment, a light
shielding film 11a is formed on the inter-layer insulating film 9
in the state of covering at least the channel parts ch of the
p-type thin film transistors p-Tr. The light shielding film 11a is
formed from, for example, aluminum (Al), titanium (Ti), tungsten
(W), silver (Ag), or an alloy thereof. Further, the light shielding
film 11a may be composed of the same layer as that of the wirings
11, and may be extended from the wirings 11 as shown in the
drawing. Besides, the light shielding film 11a may be formed in a
shape independent from the wirings 11.
In the above-mentioned manner, a so-called TFT substrate 20 is
formed.
Thereafter, like in the first embodiment, as shown in FIG. 15B, an
uncured resist film 22 is formed on the TFT substrate 20 by
application (coating), and the resist film 22 is subjected to
multi-step exposure. In this case, like in the first embodiment,
exposure may be conducted by use of a stepper having an extra-high
pressure mercury lamp as a light source, and light having a
wavelength of shorter than 260 nm may be contained in the exposure
light.
Thereafter, the resist film 22 is subjected to a developing
treatment, whereby patterning is achieved through dissolution of
the exposed portions thereof into a developing solution.
Consequently, as shown in FIG. 15C, a resist pattern 24 patterned
into a desired shape is obtained, like in the first embodiment.
The next and subsequent steps constitute a process of curing the
resist pattern 24. Now, the curing process will be described below
referring to a flowchart in FIG. 16. In this fifth embodiment, step
S2-5 is a prime, whereas steps S1 and S3 may be the same as in the
first embodiment, so that description thereof is omitted here.
First, in step S1, the substrate provided with the resist pattern
is subjected to a drying treatment. Thereafter, in step S2-5, the
resist pattern having undergone the drying treatment is irradiated
with light containing ultraviolet light in an atmosphere filled
with a dry gas. In this case, like in the first embodiment, the
irradiation is conducted in the condition where the channel parts
of the thin film transistors are prevented from being irradiated
with light having a wavelength of shorter than 260 nm. In the fifth
embodiment, the shielding of the light having a wavelength of
shorter than 260 nm is performed by use of the light shielding
film, whereas the other configurations are the same as those in
step S2-1 of the first embodiment.
Specifically, as the dry gas, an inert gas is used in the same
manner as in the first embodiment.
Besides, as the light containing ultraviolet light with which to
irradiate the resist pattern, like in the first embodiment, visible
light for enhancing the light transmittance of the heat-cured
resist pattern is preferably used together with ultraviolet light,
which is used for performing the subsequent heat curing of the
resist pattern with good shape accuracy. Therefore, as the light
source for irradiation with light, a light source which has bright
lines in the ultraviolet and visible ranges and which is suited to
irradiation of a wide area with light is used. Examples of the
light source for use here include a high pressure mercury lamp
(bright lines: 254 nm/365 nm/405 nm/436 nm/546 nm/577 nm/579 nm)
and a low pressure mercury lamp (bright lines: 185 nm/254 nm/436
nm/550 nm).
Thus, the resist pattern is irradiated with light containing
visible light together with ultraviolet light, whereby particularly
by the light shielding film provided in the peripheral region, the
channel parts of the p-type thin film transistors p-Tr are
prevented from being irradiated with light having a wavelength of
shorter than 260 nm.
Incidentally, like in the first embodiment, the step of irradiating
with light containing ultraviolet light may be carried out under a
heating condition. Besides, the treating conditions in the step of
irradiating with the light containing ultraviolet light become
parameters for controlling the ruggedness of the surface shape of
the resist pattern after heat curing, in the same manner as above.
Therefore, like in the first embodiment, it is preferable to
preliminarily detect the treating conditions such as to bring the
ruggedness of the surface shape of the heat-cured resist pattern
into a predetermined state, for example, by conducting a
preliminary experiment, and to perform the irradiation with the
light containing ultraviolet light under the treating conditions
thus detected.
Thereafter, in step S3, a heat curing treatment of the resist
pattern is conducted, in the same manner as in the first
embodiment.
Further, after the above, a liquid crystal layer LC is sandwiched
between two substrates 1 and 3, in the same manner as described
referring to FIG. 3 in the first embodiment above. As a result, a
liquid crystal display device 36' shown in FIG. 17 is obtained. The
liquid crystal display device 36' differs from the liquid crystal
display device of FIG. 3 in that the upper side of the channel
parts ch of the p-type thin film transistors p-Tr provided in the
peripheral region 1b is covered with the light shielding film 11a,
the other configurations being the same as in FIG. 3.
In this liquid crystal display device 36', the resist pattern 24'
covering the upper side of the first substrate 1 is formed as an
integral structure which buries the ruggedness on the upper side of
the first substrate 1 and which is provided with a plurality of
recessed and projected shapes at its surface.
According to the fifth embodiment as above, as has been described
referring to FIGS. 15A to 15C and 16, the step of irradiating with
the light containing ultraviolet light in an atmosphere filled with
a dry gas (step S2-5) is conducted before the step of heat curing
the resist pattern obtained by patterning through exposure and
development (step S3). This ensures that reflow of the resist
material at the time of heat curing in step S3 is prevented from
occurring, and the surface shape of the resist pattern is
maintained in the shape obtained by patterning through exposure and
development.
Accordingly, like in the first embodiment, the resist pattern
formed in an enlarged film thickness can be heat cured in the state
of retaining the rugged surface shape.
Besides, particularly in the step of irradiating with the light
containing ultraviolet light (step S2-5), as shown in FIG. 15C,
irradiation with the light h containing ultraviolet light is
conducted from the upper side of the light shielding film 11a
provided on the channel parts ch of the bottom gate type p-type
thin film transistors p-Tr, whereby the channel parts ch of the
p-type thin film transistors p-Tr are prevented from being
irradiated with light having a wavelength of shorter than 260 nm.
This ensures that degradation of characteristics of the p-type thin
film transistors p-Tr due to irradiation of the channel parts ch
with short-wavelength light can be prevented from occurring.
Consequently, by the method according to the fifth embodiment, it
is possible to obtain a liquid crystal display device 36' having
the resist pattern 24' with good heat resistance which is securely
cured in the state of retaining its shape immediately upon
lithography, without any degradation of characteristics of the thin
film transistors Tr covered with the resist pattern 24'.
Here, FIG. 18 shows transistor characteristics of the thin film
transistors beneath the resist pattern cured by applying the method
according to the fifth embodiment [IRRADIATED WITH LIGHT FROM HIGH
PRESSURE MERCURY LAMP (WITH LIGHT SHIELD)]. In this case, in step
S2-5, the resist pattern was irradiated with light from a high
pressure mercury lamp containing light having a wavelength of
shorter than 260 nm in an energy of 200 mJ, and thereafter the heat
curing treatment in step S3 was conducted. Besides, transistor
characteristics before irradiation with light [UNIRRADIATED
(REFERENCE)] is shown together.
As shown in FIG. 18, the characteristics of the thin film
transistor beneath the resist pattern having undergone a curing
treatment inclusive of irradiation with light in the condition
where a light shielding film was provided on the channel parts by
applying the fifth embodiment were confirmed to be maintained at
the characteristics before irradiation with light [UNIRRADIATED
(REFERENCE)] and be free of degradation.
<Circuit Configuration of Display>
FIG. 19 is a diagram showing an example of circuit configuration of
the active matrix type liquid crystal display devices 36, 36' shown
in the embodiments above. As shown in the diagram, the display
region 1a and the peripheral region 1b are set on the first
substrate 1 in the liquid crystal display devices 36, 36'. The
display region 1a is configured as a pixel array part in which a
plurality of scanning lines 41 and a plurality of signal lines 43
are arranged longitudinally and transversely, and one pixel is
provided correspondingly to each of intersections of the lines. In
addition, in the peripheral region 1b, a scanning line driving
circuit 15 (15-1) for scanningly driving the scanning lines 41 and
a signal line driving circuit 15 (15-2) for supplying a video
signal according to luminance information (namely, an input signal)
to the signal lines 43 are arranged.
The pixel circuit 13 provided for each of pixels corresponding to
the scanning lines 41 and the plurality of signal lines 43 includes
the above-described pixel electrode composed of the transparent
electrode 26 and the reflecting electrode 28, the thin film
transistor Tr, and a holding capacitance Cs. By driving by the
scanning line driving circuit 15-1, the video signal written from
the signal line 47 through the thin film transistor Tr is held in
the holding capacitance Cs, a voltage according to the amount of
the signal held is supplied to the pixel electrode 26, 28, and the
liquid crystal molecules constituting the liquid crystal layer are
inclined according to the voltage, whereby passage of the display
light is controlled.
Incidentally, the configuration of the pixel circuit 13 as
just-mentioned is merely an example, so that, if occasion demands,
a capacitance element may be provided in the pixel circuit 13, or a
plurality of transistors may further be provided to constitute the
pixel circuit 13. Besides, to the peripheral region 1b, a requisite
driving circuit 15 is added according to a change in the pixel
circuit 13.
APPLICATION EXAMPLE
The display according to embodiments of the present invention as
above-described is applicable to displays of electronic apparatuses
in all fields, by which a video signal inputted to the electronic
apparatus or a video signal produced in the electronic apparatus is
displayed as an image or picture, such as the electronic
apparatuses shown in FIGS. 20 to 24G, for example, digital cameras,
notebook size personal computers, PDA such as mobile phones, video
cameras, etc. Now, examples of the electronic apparatus to which
the present invention is applied will be described below.
FIG. 20 is a perspective view showing a TV set to which the present
invention is applied. The TV set pertaining to this application
example include a video display screen unit 101 composed of a front
panel 102, a filter glass 103 and the like, and is produced by
using a display according to an embodiment of the present invention
as the video display screen unit 101.
FIGS. 21A and 21B are perspective views showing a digital camera to
which the present invention is applied, wherein FIG. 21A is a
perspective view from the face side, and FIG. 21B is a perspective
view from the back side. The digital camera pertaining to this
application example includes a flash light emitting part 111, a
display part 112, a menu switch 113, a shutter button 114, and so
on, and is produced by using a display according to an embodiment
of the present invention as the display part 112.
FIG. 22 is a perspective view showing a notebook size personal
computer to which the present invention is applied. The notebook
size personal computer pertaining to this application example
includes a main body 121, a keyboard 122 operated at the time of
inputting characters and the like, a display part 123 for
displaying an image, and so on, and is produced by using a display
according to an embodiment of the present invention as the display
part 123.
FIG. 23 is a perspective view showing a video camera to which the
present invention is applied. The video camera pertaining to this
application example includes a main body part 131, an object
shooting lens 132 provided at a side surface directed forwards, a
start/stop switch 133 operated at the time of shooting, a display
part 134, and so on, and is produced by using a display according
to an embodiment of the present invention as the display part
134.
FIGS. 24A to 24G show a PDA, for example, a mobile phone to which
the present invention is applied, wherein FIG. 24A is a front view
of an opened state, FIG. 24B is a side view of the same, FIG. 24C
is a front view of a closed state, FIG. 24D is a left side view,
FIG. 24E is a right side view, FIG. 24F is a top view, and FIG. 24G
is a bottom view. The mobile phone pertaining to this application
example includes an upper-side casing 141, a lower-side casing 142,
a joint part (here, a hinge part) 143, a display 144, a sub-display
145, a picture light 146, a camera 147, and so on, and is produced
by using a display according to an embodiment of the present
invention as the display 144 and/or the sub-display 145.
Incidentally, while configurations in which the present invention
is applied to a liquid crystal display device have been described
in the embodiments above, the present invention is applicable also
to a display configured by arranging organic electroluminescence
elements (so-called organic EL display). In this case, the resist
film described in the above embodiments is applied as an insulating
film covering a display region where the organic
electroluminescence elements are provided.
It should be understood by those skilled in the art that various
modifications, combinations, sub-combinations and alterations may
occur depending on design requirements and other factors insofar as
they are within the scope of the appended claims or the equivalents
thereof.
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